Method and arrangement for layout of gridless nonManhattan semiconductor integrated circuit designs

ABSTRACT

The present invention introduces several methods for laying out integrated circuit designs that use gridless non Manhattan routing to connect the integrated circuit components. In one embodiment, the non Manhattan routed integrated circuit designs are laid out by creating an initial route and then compacting the design down. In another embodiment, gridless non Manhattan integrated circuits are laid out by adapting a gridless Manhattan routing system into a gridless non Manhattan routing system by rotating a plane of a tile based maze router.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. PatentApplication entitled “Method And Arrangement For Layout And ManufactureOf Gridless Non Manhattan Semiconductor Integrated Circuits,” filed onJun. 3, 2001, and having the Ser. No. 09/681,775, now U.S. Pat. No.6,711,727.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor design andmanufacture. In particular the present invention discloses gridlesssemiconductor architectures and methods for designing and manufacturinggridless semiconductor integrated circuits.

BACKGROUND OF THE INVENTION

An integrated circuit (“IC”) is a semiconductor device that includesmany electronic components (e.g., transistors, diodes, inverters, etc.).These electrical components are interconnected to form larger scalecircuit components (e.g., gates, cells, memory units, arithmetic units,controllers, decoders, etc.) on the IC. The electronic and circuitcomponents of IC's are jointly referred to below as “components.”

An IC also includes multiple layers of metal and/or polysilicon wiringthat interconnect its electronic and circuit components. For instance,many IC's are currently fabricated with five metal layers. In theory,the wiring on the metal layers can be all-angle wiring (i.e., the wiringcan be in any arbitrary direction). Such all-angle wiring is commonlyreferred to as Euclidean wiring. In practice, however, each metal layertypically has a preferred wiring direction in an attempt to maximize thenumber of signal wires placed on each wiring layer by preventingintersections. In current ICs, the preferred direction alternatesbetween successive metal layers. Most IC's use the “Manhattan” wiringmodel, which specifies alternating layers of preferred-directionhorizontal and vertical wiring. (Viewed from above, the horizontal andvertical wiring resemble the orthogonal streets of Manhattan.) In theManhattan wiring model, essentially all of the interconnect wires arehorizontal or vertical.

Design engineers design IC's by transforming circuit description of theIC's into geometric descriptions, called layouts. To create anintegrated circuit layout, design engineers typically use electronicdesign automation (“EDA”) applications. These EDA applications providesets of computer-based tools for creating, editing; and analyzing ICdesign layouts. EDA applications create layouts by using geometricshapes that represent different materials and devices on IC's. Forinstance, EDA tools commonly use rectangular lines to represent the wiresegments that interconnect the IC components. These EDA tools alsorepresent electronic and circuit IC components as geometric objects withvarying shapes and sizes. For the sake of simplifying the discussion,these geometric objects are shown as rectangular blocks in thisdocument. Also, in this document, the geometric representation of anelectronic or circuit IC component by an EDA application is referred toas a “circuit module.”

EDA applications typically illustrate circuit modules with electricalinterface “pins” on the sides of the circuit modules. These pins connectto the interconnect lines, the “wiring” used to connect the variouscircuit modules. A collection of pins that are, or need to be,electrically connected is referred to as a net.

FIG. 1 illustrates a simple example of an IC layout 100. The IC layout100 includes five circuit modules 105, 110, 115, 120, and 125 with pins130-160. Four interconnect lines 165-180 connect these modules throughtheir pins. In addition, five nets specify the interconnection betweenthe pins. Specifically, pins 35, 45, and 60 define a three-pin net,while pins 30 and 55, and pins 40 and 50 respectively define two two-pinnets. As shown in FIG. 1, a circuit module (such as 105) can havemultiple pins on multiple nets.

The IC design process entails various operations. FIG. 2 illustrates theoverall process for laying out an integrated circuit device once thelogical circuit design of the integrated circuit device has beencompleted. Some of the physical-design operations that EDA applicationscommonly help perform to layout an integrated circuit include: (1) floorplanning (in step 210 of FIG. 2), which divides the integrated circuitlayout area into different sections devoted to different purposes (suchas ALU, memory, decoding, etc.); (2) placement (in step 220 of FIG. 2),which finds the alignment and relative orientation of the circuitmodules; (3) global and detailed routing (in steps 230 and 240 of FIG.2), which completes the interconnects between the circuit modules asspecified by the net list; (4) compaction (in step 250 of FIG. 2), whichcompresses the layout in all directions to decrease the total IC area;and (5) verification (in step 250 of FIG. 2), which checks the layout toensure that it meets design and functional requirements.

Referring to step 210 of FIG. 2, layout designers initially performhigh-level floor planning. During the high-level floor planning, layoutdesigners decide roughly where various large circuit blocks will beplaced on the integrated circuit. The layout designers then perform a“placement” step 220. During the placement step, the layout designersplace all the circuit cells into specific locations while following thehigh-level floor planning map of step 210. The placement step 220 islargely performed with the help of EDA tools that help select optimizedplacement. FIG. 3 a illustrates an example of two large circuit modules310 and 320 and two smaller circuit modules 330 and 340 placed onto anintegrated circuit layout. The various circuit modules may be rotatedninety degrees as necessary to obtain a desired layout.

Operation (3), routing, is generally divided into two sub steps: globalrouting (step 230 of FIG. 2) and detailed routing (step 240 of FIG. 2).Global routing divides an integrated circuit into individual globalrouting areas. Then, a global routing path is created for each net bylisting the global routing areas that the net must pass through. Afterglobal routes have been created, each individual global routing area isthen processed with detailed routing. Detailed routing creates specificindividual routing paths for each net within that global routing area.

Global routing is a step that is used to divide an extremely difficultoverall routing problem into smaller routing problems in a “divide andconquer” approach. The overall task of routing an integrated circuit isto route together all electrically common signals on the integratedcircuit. The global routing step divides an integrated circuit area intoindividual global routing areas and then determines the specific globalrouting areas that each electrically common signal must pass through.The list of circuit modules and pins that need to be connected for aspecific electrically common signal is known as a net. The contiguouspath through the global routing areas is known as a “global routingpath” for that net. An example of global routing is provided withreference to FIGS. 3 a and 3 b.

Referring to FIG. 3 a, there are three different electrically commonsignals A, B, and C. The electrical signal terminations for electricallycommon signals A, B, and C illustrated on FIG. 3 a as marked dots. Theelectrical signal terminations are commonly referred to as “pins”.Furthermore, the integrated circuit of FIG. 3 a has been divided intosixteen different global routing areas that are labeled 01 to 16. Foreach electrically common signal, a net is created containing a list ofall the global routing areas that have common electrical signaltermination pins. Thus, for example, the net of electrical signal A is01, 02, 08, and 12 since electrical signal A has termination pins inthose labeled global routing areas.

After creating the various nets, global routing path lists are thenconstructed from the various nets. FIG. 3 b illustrates the integratedcircuit of FIG. 3 a with the addition of global routing path lists androughly sketched global routing paths. (The actual specific routing pathis not determined during the global routing step, just the list ofglobal routing areas that a signal must enter or pass through.) Theglobal routing paths join together global routing areas in the nets withadditional global routing areas such that all global routing areas inthe global routing path list form a contiguous global routing path. Notethat each net may have many different possible global routing paths. TheElectronic Design Automation (EDA) software attempts to select theglobal routing paths that are close to optimal.

Referring back to the flow diagram of FIG. 2, detailed routing isperformed at step 240 for the various global routing areas. In thedetailed routing process, each electrical interconnect signal line thatpasses through or terminates within a particular global routing areamust be given a specific routing path within that global routing area.Generally, detailed routing systems use a routing grid that specifies avery limited set of possible locations for the various electricalinterconnect signals. Adjacent electrical interconnect signals in agridded detailed routing system are separated by a worst-case distancethat will ensure that adjacent electrical interconnect signals are notshorted together during the manufacturing process.

The routing example illustrated in FIGS. 3 a and 3 b requires severaldetailed routing tasks to be performed. For example, the detailedrouting for global routing area 06 requires that electrical interconnectsignal B pass from the left side to the right side of the global routingarea and electrical interconnect signal C enter from the bottom andterminate at a pin on large circuit module 310. FIG. 3 c illustrates anexample of one possible detailed route for global routing area 06. Notethat the detailed electrical interconnect signal routes illustrated inFIG. 3 c follow the prescribed routing grid that is illustrated withdashed lines. The vertical and horizontal interconnect lines are ondifferent layers such that there is no electrical connection at placeswhere the interconnect wires cross unless a via has been created at thatlocation. In most cases, many different possible detailed routing pathsexist. For example, FIG. 3 d illustrates just one alternate detailedelectrical interconnect signal routing for global routing area 06 of thelayout illustrated in FIGS. 3 a and 3 b.

Since the global routing step 230 divided the overall routing probleminto many smaller routing problems, the detailed routing of eachindividual global routing area is simplified. If a particular detailedrouting problem is unsolvable, the system may return to step 230 inorder to get a different global routing solution and then attemptdetailed routing on the new global routing solution. Thus, routing anintegrated circuit is often an iterative process.

Referring back to FIG. 2, after the routing steps have been performed,the integrated circuit layout is tested and optimized at step 250.Common testing and optimization steps include extraction, verification,and compaction. The steps of extraction and verification are performedto ensure that the integrated circuit layout will perform as desired.Compaction allows designers to reduce the size of an integrated circuitdesign in order to improve performance. Furthermore, a compacted designlowers costs by allowing more integrated circuits to be produced for agiven wafer size. Finally, the tested and optimized integrated circuitis manufactured at step 290. Note that problems may occur during varioussteps of the integrated circuit layout forcing the designers to returnto earlier steps.

The task of routing a typical integrated circuit is a very difficulttask due to the large number of interconnect lines that must be routedand the extremely large number of possible different routing paths. Tosimplify the routing task, most automated routing systems use a griddedsystem wherein the number of possible positions of interconnect signalsis sharply limited to a specific set wiring grid. However, a gridlessrouting system that allows interconnect signal wires to be placedanywhere can provide better routing since it is not limited by theartificial routing grid restriction. Thus, to provide highly optimizedinterconnect line routing, it is desirable to implement gridlessintegrated circuit architectures.

SUMMARY OF THE INVENTION

The present invention introduces several methods for implementinggridless non Manhattan routing systems for integrated circuitmanufacture. In a first embodiment, a gridless non Manhattan routingsystems may be implemented by compacting a gridded non Manhattan design.In another embodiment, a gridless non Manhattan routing systems may beimplemented by adapting a gridless Manhattan routing system by rotatinga plane of a tile based maze router.

The present invention further discloses non Manhattan routing systemsthat use simulated Euclidean wiring. Entire routing layers may beimplemented with arbitrary angle preferred wiring using simulatedEuclidean wiring.

Other objects, features, and advantages of present invention will beapparent from the company drawings and from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, and advantages of the present invention will beapparent to one skilled in the art, in view of the following detaileddescription in which:

FIG. 1 illustrates an example of an integrated circuit layout.

FIG. 2 illustrates a flow diagram describing the steps performed whenlaying out an integrated circuit design.

FIG. 3 a illustrates an example of circuit placement for an integratedcircuit layout along with nets for common electrical signals.

FIG. 3 b illustrates one possible global routing for the exampleintegrated circuit of FIG. 3 a.

FIG. 3 c illustrates one possible detailed route for global routing area06 of the example integrated circuit of FIG. 3 b.

FIG. 3 d illustrates one possible detailed route for global routing area06 of the example integrated circuit of FIG. 3 b.

FIG. 4 a illustrates the top view of a multiple layer integrated circuitthat uses a non Manhattan diagonal wiring model.

FIG. 4 b illustrates a side view of various different types of multiplelayer integrated circuits that start with two Manhattan layers.

FIG. 4 c illustrates a side view of various different types of multiplelayer integrated circuits that start with three Manhattan layers.

FIG. 5 illustrates an example of a Manhattan routing grid with exampleelectrical signal lines.

FIG. 6 a illustrates a first proposed gridded non Manhattan layer on topof a Manhattan routing grid.

FIG. 6 b illustrates a second proposed gridded non Manhattan layer ontop of a Manhattan routing grid.

FIG. 7 illustrates an example of a 45° angle diagonal routing grid thathas been superimposed on a Manhattan routing grid wherein both routinggrids have the same pitch.

FIG. 8 illustrates an example of a situation where three interconnectlines intersect and a fourth interconnect line is relatively close.

FIG. 9 illustrates a close-up view of the area indicated by large circle730 in FIG. 7.

FIG. 10 a illustrates a gridded wiring system that separatesinterconnect lines by a worst-case distance.

FIG. 10 b illustrates a section of detailed routing in a compactedgridless system.

FIG. 10 c illustrates a simplified integrated circuit constructed with agridless non Manhattan wiring system.

FIG. 11 illustrates a Manhattan two-dimensional tiling structureoverlaid with a non Manhattan two-dimensional tiling structure.

FIG. 12 illustrates a flow diagram that describes one method ofperforming compaction on a routing layout that includes non Manhattanlayers of interconnect lines.

FIG. 13 a illustrates a layout section of non Manhattan interconnectwiring that has not been compacted yet.

FIGS. 13 b through 13 k illustrate the layout section of non Manhattaninterconnect wiring of FIG. 13 a as it is compacted.

FIG. 13 l illustrates the layout section of non Manhattan interconnectwiring of FIG. 13 a after it has been compacted.

FIG. 14 illustrates a sorted relative vertical position graph of all thehorizontal and diagonal interconnect lines from FIG. 13 a.

FIG. 15 illustrates a sorted relative horizontal position graph of allthe vertical interconnect lines and diagonal interconnect lines fromFIG. 13 a.

FIGS. 16 a to 16 f illustrate the vertical compaction of interconnectlines around an obstacle.

FIG. 17 a illustrates a first angled wire created with a griddedManhattan system.

FIG. 17 b illustrates a second angled wire created with a griddedManhattan system.

FIG. 17 c illustrates the angled wire of FIG. 17 a created with agridless Manhattan system.

FIG. 17 d illustrates a first angled wire with an angle between theangle of FIG. 17 a and the angle of FIG. 17 b created with a gridlessManhattan system.

FIG. 17 e illustrates a first angled wire with an angle between theangle of FIG. 17 a and the angle of FIG. 17 b created with a gridless noManhattan system.

FIG. 17 f illustrates the angled wire of FIG. 17 b created with agridless Manhattan system.

FIG. 18 a illustrates a first angled wire created with a gridded nonManhattan system.

FIG. 18 b illustrates a second angled wire created with a gridded nonManhattan system.

FIG. 18 c illustrates the angled wire of FIG. 18 a created with agridless non Manhattan system.

FIG. 18 d illustrates a first angled wire with an angle between theangle of FIG. 18 a and the angle of FIG. 18 b created with a gridlessnon Manhattan system.

FIG. 18 e illustrates a first angled wire with an angle between theangle of FIG. 18 a and the angle of FIG. 18 b created with a gridlessnon Manhattan system.

FIG. 18 f illustrates the angled wire of FIG. 18 b created with agridless non Manhattan system.

FIG. 19 a illustrates a first method of calculating the lengths of a 45°angle diagonal interconnect line segment and a horizontal interconnectline segment to simulate a Euclidean interconnect line segment with anangle A.

FIG. 19 b illustrates a second method of calculating the lengths of a45° angle diagonal interconnect line segment and a horizontalinterconnect line segment to simulate a Euclidean interconnect linesegment with an angle A.

FIG. 20 illustrates alternating pairs of horizontal interconnect linesand diagonal interconnect lines used to create a close approximation toa desired arbitrary angle interconnect line with angle A.

FIG. 21 illustrates an example metal layer containing an arbitrarypreferred angle layer that is approximated with a collection ofManhattan (horizontal or vertical) and 45° angle diagonal interconnectline segments on the same layer.

FIG. 22 illustrates a side view of three different types of multiplelayer integrated circuits that start with two Manhattan layers andinclude simulated Euclidean layers.

FIG. 23 illustrates a side view of three different types of multiplelayer integrated circuits that start with three Manhattan layers andinclude simulated Euclidean layers.

FIG. 24 illustrates a top view of an integrated circuit with Manhattanlayers that are diagonal with respect to the integrated circuit edges.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Gridless non Manhattan integrated circuit (“IC”) architectures andmethods for designing and manufacturing gridless non Manhattanintegrated circuits are disclosed. In the following description, forpurposes of explanation, specific nomenclature is set forth to provide athorough understanding of the present invention. However, it will beapparent to one skilled in the art that these specific details are notrequired in order to practice the present invention. For example, thepresent invention has mainly been described with reference to a nonManhattan routing system that uses two layers of orthogonal 45° anglewiring and a non Manhattan routing system that uses plus 60° anglewiring and negative 60° wiring. However, the same techniques can easilybe applied to many other types of gridless non Manhattan routingsystems.

Routing Architectures

Most existing semiconductors use the “Manhattan” wiring model thatspecifies alternating layers of preferred-direction horizontal andvertical wiring. In the Manhattan wiring model, the majority of theinterconnect signals are horizontal or vertical. However, occasionaldiagonal jogs are sometimes allowed on the preferred horizontal andvertical layers.

The Manhattan wiring model has proven to be useful, but it is certainlynot optimal. Distant pins must often be connected by long stretches ofconnected horizontal and vertical interconnect signals. To provide amore optimal system, a related patent application title“Multi-Directional Wiring On A Single Metal Layer”, filed on Dec. 12,2000 and having Ser. No. 09/733,104, incorporated by reference, uses anon Manhattan wiring model that uses diagonal wiring as a “preferred”direction for some layers. For purposes of nomenclature, a “preferred”direction is defined as the direction that at least 40 percent of thewires are configured. Interconnect lines are considered “diagonal” ifthey form an angle other than zero or ninety degrees with respect to thelayout boundary of the IC.

In one embodiment, the diagonal wiring consists of wires deposed at plus45 degrees or minus 45 degrees (referred to herein as “octalinear”).This architecture is referred to as octalinear wiring in order to conveythat an interconnect line can traverse in eight separate directions fromany given point. In another embodiment, wires are deposed at plus 60degrees or minus 60 degrees (referred to herein as “hexalinear”).Although the use of the diagonal wiring in the present invention isdescribed in conjunction with wires arranged at plus 45, minus 45, plus60, and minus 60 degrees; any angle offset from zero and 90 degrees(horizontal or vertical) may be used as diagonal wiring withoutdeviating from the spirit or scope of the invention. In one embodiment,the preferred wiring angle is selected based upon the neededinterconnections.

In general, metal layers on integrated circuit are typically organizedin perpendicular metal layer pairs. The use of perpendicular metal layerpairs minimizes wiring distances by minimizing the number of layers awire or via must transverse to get to a layer with wires disposed in anorthogonal direction. In addition, the use of perpendicular wiring inadjacent layers eliminates wires routed in parallel on adjacent layers,thus reducing electrical coupling between metal layers and minimizesnoise interference.

Some embodiments of the present invention are described using“complementary” pairs of wiring layers. As used herein, complementarypairs refer to two wiring layers with a preferred wiring directionperpendicular to one another or close to perpendicular to each other.For example, a complementary layer to a vertical wiring layer is ahorizontal wiring layer. In diagonal wiring, a complementary directionto a plus 45 degree wiring direction is a negative 45 degree wiringdirection. Similarly, a complementary direction to a negative 60 degreewiring direction may be a plus 60 degree wiring direction. An alternateembodiment may have a complementary direction to a negative 60° wiringdirection as a plus 30° wiring direction.

FIG. 4 a illustrates the top view of an example integrated circuit(“IC”) that has multiple metal layers wherein some of the metal layersemploy diagonal wiring. In the embodiment of FIG. 4 a, the IC layoututilizes horizontal, vertical, and 45° diagonal interconnect linelayers. The horizontal interconnect lines are the lines that areparallel to the x-axis (i.e., the horizontal lines are at 0° to thex-axis and parallel to the length of the layout). The verticalinterconnect lines are the lines that are perpendicular to the x-axis(i.e., the vertical lines are at 90° to the x-axis). Furthermore, in theembodiment of FIG. 4 a, one set of diagonal lines (layer 3) are at +45°with respect to the length of the IC layout, while another set (layer 4)are at −45° with respect to the length of the IC layout.

In the particular example of FIG. 4 a, there are four metal (or wire)layers that carry interconnect signals. As shown in FIG. 4 a, thehorizontal wires in layer one are designated with the short dashed line,the vertical wires in layer two are designated with a longer dashedline, the +45° diagonal wires in layer three are designated with a solidline, and the −45° diagonal wires in layer four are designated withalternating long-short dashed lines. The wires on different nets in aspecific layer generally do not touch or cross other wires in that samelayer since that would cause an electrical short of the two nets.However, an occasional “zag” may not follow the preferred wiringdirection.

As shown in FIG. 4 a, layer one wires, such as wire 130, have apredominant or “preferred” horizontal direction. The wires in layer oneare situated horizontally such that the wires run parallel to the topand bottom of integrated circuit 100. The wires in layer two have apreferred vertical direction (e.g., wire 120 is situated in a verticaldirection relative to the top and bottom of the integrated circuit chip100). Thus, for this example, metal layers one and two are Manhattanlayers with horizontal and vertical preferred directions, respectively.

For the example of FIG. 4 a, layers three and four employ diagonalwiring. Specifically, layer three has a preferred diagonal direction(i.e., plus 45°) relative to the top and bottom of integrated circuit100. Interconnect wire 140 is an example layer three wire that isoriented in a diagonal direction. Layer four has a preferred diagonaldirection that is negative 45° relative to the top and bottom ofintegrated circuit 100. Interconnect wire 150 is example of a layer fourwire situated at minus 45°.

The example embodiment of FIG. 4 a also includes a plurality of vias. Ingeneral, vias provide an electrical conductor between metal layers topermit routing between the metal layers in the integrated circuit. Thecircles illustrated in FIG. 4 a depict vias that connect interconnectwires on different metal layers. For example, via 110 electricallyconnects a vertical wire 111 on layer two to a diagonal wire 113 onlayer four. Similarly, several vias are shown in the example of FIG. 4 ato couple wires: between Manhattan layers, between diagonal layers, andbetween Manhattan and diagonal layers.

The use of diagonal wiring more efficiently routes wires in anintegrated circuit by reducing the length of the required interconnectwires. Many different combinations of wiring layers may be used. FIG. 4b illustrates a variety of multiple layer wiring configurations.Specifically, FIG. 4 b illustrates a side view of an integrated circuitimplemented using Manhattan geometries for the first two metal layers(layers one and two). In one embodiment, level one has a preferredhorizontal direction and level two has a preferred vertical directionthat is complementary to the horizontal direction of level one. Inalternate embodiment, level one has a preferred vertical direction andlevel two has a preferred horizontal direction that is complementary tothe vertical direction of level one. The use of horizontal and verticalpreferred directions for layers one and two is desirable since manyexisting circuit libraries are designed for integrated circuits thatwill have horizontal and vertical preferred wiring for layers one andtwo. As illustrated in FIG. 4 b, many different types of metal layersmay be placed on top of the first two Manhattan metal layers.

FIG. 4 c illustrates a side view of an integrated circuit implementedusing Manhattan geometries for the first three metal layers (layers one,two, and three). The use of horizontal and vertical preferred directionsfor the first three layers is desirable since some complex libraries aredesigned for integrated circuits that have three Manhattan layers. Thefirst three layers may be horizontal, vertical, horizontal (HVH); orvertical, horizontal, vertical (VHV).

Non Manhattan Routing

Most place and route EDA systems use a “gridded” Manhattan routingarchitecture wherein the interconnect signal lines are only placed ontoa predefined two-dimensional routing “grid” of horizontal and verticalrouting paths that is imposed by the routing system. The routing griddefines a specific set of paths (or channels) that may carry aninterconnect signal line. The possible routing paths of the routing gridare separated by a defined worst-case minimum distance that ensures thatadjacent signal lines will not be shorted together during themanufacturing process.

Non Manhattan Wiring

The horizontal and vertical lines of FIG. 5 define an example routinggrid in a Manhattan based routing system. Thus, to connect any twopoints in a gridded system, a path along the horizontal and verticalrouting grid lines must be chosen. For example, to connect point A1 topoint A2 on the routing grid of FIG. 5, horizontal interconnect line 510and vertical signal line 520 may be used. The horizontal interconnectline 510 and vertical interconnect line 520 segments are generally ondifferent metal layers and are connected by a via 530. In a griddedrouting system, vias are generally required to be at the gridintersections such that horizontal and vertical signal lines may beinterconnected.

To shorten the interconnect signal paths and allow higher densitywiring, a gridded non Manhattan wiring system allows point A1 to beconnected to point A2 with a diagonal interconnect line 540. However, itshould be noted that the diagonal interconnect signal lines of the nonManhattan layers in a gridded system should also pass through the samerouting grid intersections such that the interconnect lines of the nonManhattan layers may be connected to the signal lines of the Manhattanlayers. As illustrated in FIG. 5, the distance along diagonalinterconnect line 540 is shorter than the distance along horizontalinterconnect line 510 and vertical interconnect line 520. Thus, anintegrated circuit built with diagonal interconnect line 540 wouldexhibit a shorter propagation delay along diagonal interconnect line 540than an integrated circuit built with horizontal interconnect line 510and vertical interconnect line 520.

Gridded Non Manhattan Routing

FIG. 6 a illustrates a grid for the Manhattan layers with a few diagonallines for a proposed 45° angle non Manhattan layer. Note that all theproposed 45° angle non Manhattan layer interconnect lines pass throughthe intersection points of the Manhattan layer interconnect lines.However, the distance between the proposed adjacent 45° angleinterconnect lines is less than the minimum distance requirement “dmin”.(Specifically, the distance between the adjacent proposed 45° angleinterconnect lines is $\frac{d\quad\min}{2}.$Thus, the proposed 45° angle non Manhattan layer of FIG. 6 a will cannotbe manufactured reliably.Gridded Non Manhattan Wiring with Exact Intersection Vias

To have a gridded 45° angle non Manhattan layer operate properly, theadjacent 45° angle interconnect lines must be separated by a distancegreater than or equal to minimum distance “dmin”. Thus, FIG. 6 billustrates a functional gridded 45° angle non Manhattan layer whereinthe distance between adjacent parallel signal lines is √{square rootover (2)}*dmin in order to satisfy the minimum distance “dmin”requirement. The gridded 45° angle non Manhattan layer illustrated inthe lower right of FIG. 6 b is less than optimal since the interconnectline density is significantly lower than the gridded Manhattan layers.However, the interconnect line density may be greatly improved usingcompaction as will be described in detail in a later section of thisdocument.

Gridded Non Manhattan Wiring with Inexact Intersection Vias

In an alternate gridded non Manhattan system, the gridded non Manhattanwiring layers are arranged in a manner that does not explicitly attemptto align the non Manhattan interconnect grid lines with theintersections of the Manhattan grid layers. FIG. 7 illustrates such analternate gridded non Manhattan wiring embodiment. In the embodiment ofFIG. 7, a +/−45° angle diagonal routing grid has been superimposed on astandard horizontal and vertical Manhattan routing grid. (Note that eachdifferent wiring direction is on an independent wiring layer.) Both theManhattan routing grid (horizontal and the non Manhattan (+/−45° anglediagonal, in this example) routing grid have the same grid pitch. Thus,the diagonal interconnect lines do not all line up with theintersections of the Manhattan routing grid layers.

However, by examining the Manhattan routing grid and the non Manhattanrouting grid of FIG. 7, it can be seen that at a large number oflocations, three or more interconnect grid lines align very closely.Each of these positions has been marked with a small circle. At suchpositions, a via could be created thus allowing any of those three (orfour) interconnect lines to be coupled. For example, at location 710, aninterconnect line from the horizontal, vertical, or −45° diagonalinterconnect layer can be coupled together. Thus, although not everyintersection is available for connecting different layers, a sufficientnumber of vias positions are available to allow such a gridded nonManhattan routing system to be very useful. It should be noted that mostgrid layer intersections do not have vias for connecting the layers.

Close Intersection Via Connections with Zags

In addition to the locations where three or more interconnect linesmeet, there are several locations where three or more interconnect linescome relatively close to intersecting. The larger circles on FIG. 7highlight these situations. At such locations, a small section ofinterconnect line may go in a direction other than the layer's preferreddirection to couple that interconnect line to a via. For example, thearea indicated by large circle 720 is an area where three of theinterconnect lines intersect and a fourth interconnect line isrelatively close. An enlarged view of the situation in circle 720 isillustrated in FIG. 8.

As illustrated in FIG. 8, a horizontal interconnect line 810, a verticalinterconnect line 820, and a first diagonal line 830 all intersect at agood via location 890. Thus, a via at location 890 could connected anyof those three layers. A second diagonal interconnect line 840 isrelatively close to the via at location 890 but does not intersect it.To connect the second diagonal interconnect line 840 a short diagonal“zag” 870 (an interconnect line that is not in the layer's preferreddirection) connects second diagonal interconnect line 840 to the via atlocation 890. Thus, even in situations where the interconnect lines donot exactly align to form an intersection, a via may be used if theinterconnect lines are sufficiently close to each other such that a zagcan be used to connect interconnect lines that do not exactly cross theintersection.

Referring back to FIG. 7, it can be seen that in a gridded non Manhattansystem there are a sufficiently large number of situations where theinterconnect lines are close enough that a requirement of aligned vialocations is not necessary. Not that the situations wherein the gridlines from different layers intersect at exactly the same position (suchas location 710) are a special case wherein the needed “zag” is oflength zero.

Opportunistic Connection Gridded System

A gridded non Manhattan routing system may relax the requirement thatall interconnect lines meet as specific grid points. Such a system mayinstead allow any desired routing grid for any layer provided that itmeets the minimum distance guidelines. In such a system, the griddedrouting system may keep track of every location where interconnect linesfrom different layers cross each other. At any such crossing location,the gridded non Manhattan routing system may create a via toelectrically couple the interconnect wires on those two layers providedthat no interconnect line on any other layer is affected by the via.Such a system may be referred to as an “opportunistic connection griddedsystem.”

Referring to FIG. 7, the area indicated by large circle 730 is an areawhere three of the gridded interconnect lines on three different layerscome relatively close to intersecting. FIG. 9 illustrates a close-upview of the area indicated by large circle 730 in FIG. 7. As illustratedin FIG. 9, there is no single location where all three interconnectlines intersect.

However, an “opportunistic connection” routing system can makeelectrical connections between any of the three interconnect line layersas illustrated in FIG. 9 where there is an opportunity for such aconnection. Specifically, horizontal interconnect line 910 on thehorizontal layer and vertical interconnect line 920 on the verticallayer may be connected by a via at location 990; horizontal interconnectline 910 on the horizontal layer and diagonal interconnect line 930 onthe diagonal layer may be connected by a via at location 980; andvertical interconnect line 920 on the vertical layer and diagonalinterconnect line 930 on the diagonal layer may be connected by a via atlocation 970. Thus, a sophisticated gridded non Manhattan “opportunisticconnection” routing system may be implemented by determining where anytwo interconnect lines on different layers cross each other and placingvias in such locations as necessary to implement the desiredinterconnections.

Gridless Non Manhattan Routing Architecture

To improve upon the interconnect line density, the present inventionfurther proposes a gridless non Manhattan routing architecture. Thegridless non Manhattan routing architecture does not restrict theplacement of interconnect signal lines to specific paths on a routinggrid. In a gridless non Manhattan routing system, interconnect wires maybe placed in almost any position and at almost any angle provided thatthe interconnect wires are placed far enough apart so that theinterconnect wires can be manufactured reliably and there is notundesired interference between nearby interconnect wires.

One slight limitation on interconnect wiring placement is that a“manufacturing grid” imposed by the integrated circuit manufacturingprocess slightly limits the placement locations of interconnect wiring.However, the manufacturing grid is generally not much of a limitationsince the pitch of the manufacturing grid is generally much smaller thanthe width of an individual interconnect wire. For example, themanufacturing grid may be on the order of 1 nanometer while the width ofan individual interconnect wire may be an order of magnitude larger.

Gridless Routing Advantages

A gridless routing system provides interconnect line density improvementover a gridded system on all wiring layers. The reason for this is thatgridded routing systems are based upon a worst cast assumption. Forexample, FIG. 10 a illustrates a detailed Manhattan routing grid for aglobal routing area. The routing grid of FIG. 10 a contains twointerconnect signals 1010 and 1020. To the two different electricalinterconnect signals from being connected together, the conductorsassociated with interconnect signals 1010 and 1020 must be separated byat least a minimum distance of dmin such that the integrated circuit maybe manufactured reliably. However, the interconnect signals 1010 and1020 may also have adjacent “landing pads” 1015 and 1025 for vias asillustrated in FIG. 10 a. Thus, the interconnect signals 1010 and 1020must be separated by a wider “worst case” distance dpitch(gridded) thatensures a minimum distance of dmin between the two adjacent via landingpads 1015 and 1025 illustrated in FIG. 10 a. The gridded system with thespacing illustrated in FIG. 10 a is known as gridded system with“via-to-via” spacing.

Thus, as illustrated in FIG. 10 a, a via-to-via gridded wiring systemmust separate interconnect lines by the wide worst-case distance ofDpitch(gridded) since the two adjacent interconnect signals 1010 and1020 may have adjacent via landing pads 1015 and 1025 as illustrated inFIG. 10 a. This worst case scenario wastes space when the worst case isnot present. For example, in a gridded system, adjacent interconnectsignals 1013 and 1022 with non adjacent via landing pads 1017 and 1027must still be separated by the wide worst-case distance ofDpitch(gridded) even though this creates a space much larger than dminbetween any conductor associated with interconnect signals 1013 and1022.

With a gridless system, the potential worst-case scenarios do not havehinder the entire integrated circuit layout. FIG. 10 b illustrates asection of detailed routing in a gridless system. (A routing grid isillustrated in FIG. 10 b to allow comparisons between the gridlesssystem of FIG. 10 b and the gridded system of FIG. 10 a.) Referring toFIG. 10 b, when two adjacent interconnect lines 1030 and 1040 have nonadjacent landing pads 1035 and 1045, those interconnect lines 1030 and1040 can be placed adjacent with a pitch of Dpitch(gridless1) that issmaller than Dpitch(gridded) of FIG. 10 a. Thus, an improved wiringdensity is achieved with a gridless system. The pitch ofDpitch(gridless1) ensures that the minimum distance dmin exists betweenthe landing pad 1035 and interconnect line 1040.

Certain gridded systems allow the closer spacing illustrated by theDpitch(gridless1) example in FIG. 10 b by forbidding vias to be ever beadjacent to each other. Such a gridded routing system is a known as agridded routing system with “line-to-via” spacing. A line-to-via spacinggridded routing system provides better interconnect line density than avia-to-via gridded routing system. However, this improved density comesat the expense of completely forbidding adjacent vias.

A gridless routing system can provide even further improved interconnectline density than a line-to-via gridded system. If there are no landingpads or other obstacles on a pair of adjacent interconnect wires, thenthe pitch between adjacent interconnect wires can be even smaller.Specifically, FIG. 10 b illustrates interconnect lines 1050 and 1060separated by a pitch of Dpitch(gridless2) that is equal to the minimumdistance dmin. Such a gridless routing system is said to have“line-to-line” spacing. Such a system provides the highest achievableinterconnect line density.

Furthermore, with a gridless system, esoteric routing patterns can becreated that optimize the layout area. For example, FIG. 10 billustrates interconnect line 1042 connected to landing pad 1047 withinterconnect line 1032 neatly following the contour of interconnect line1042 and landing pad 1047 to conserve integrated circuit die area. Thus,using a gridless system can greatly improve wiring density in all metalwiring layers of an integrated circuit.

Gridless Non Manhattan Routine

By combining a gridless routing architecture with non Manhattan wiringlayers, the present invention allows very efficient wiring to be createdfor integrated circuits. FIG. 10 c illustrates a simplified integratedcircuit constructed with a gridless non Manhattan wiring system. Sincethe routing system is gridless, adjacent interconnect lines may beplaced as close together as possible provided that there is nointerference between the adjacent lines and the adjacent interconnectlines can be manufactured reliably. Furthermore, since the routingsystem used in FIG. 10 c allows non Manhattan layers, diagonalinterconnect lines can be used to create the shortest possible pathsbetween modules that need to be connected. For example, referring againto FIG. 10 c, module 1093 and module 1097 are coupled with 45° diagonalinterconnect lines since those 45° diagonal interconnect lines providethe shortest possible path between those two circuit modules.

To create a gridless non Manhattan integrated circuit layout, a gridlessnon Manhattan routing tool may be used. Such a gridless non Manhattanrouting tool may be created by modifying an existing gridless Manhattanrouting tool to accommodate diagonal wiring.

For example, the gridless Manhattan routing tool proposed by Jeremy Dionand Louis M. Monier in their paper “Contour: A Tile-based GridlessRouter” (Digital Western Research Laboratory Report 95/3) can beextended to handle diagonal interconnect lines in order to create agridless non Manhattan routing tool. Their gridless Manhattan routingtool used an automatic maze router based on a corner-stitching datastructure. Their router uses a collection of two-dimensional planeswherein each plane comprises a set of rectangular tiles representingcircuit geometry or free space between circuit geometry.

To extend their gridless Manhattan routing tool into a gridless nonManhattan routing tool, sets of rotated tiling planes are added. FIG. 11illustrates a first Manhattan tiling plane 1110 along with asuperimposed non Manhattan tiling plan 1150. The maze router may routesignals on any plane provided that the signals may be interconnectedwith a via as needed. In the illustration of FIG. 11, there must beenough room for a via 1150 in both the available tile on the Manhattantiling plane 1110 and the tile on the non Manhattan tiling plan 1150that overlaps the Manhattan tile.

Similarly, the gridless Manhattan routing tool proposed by Hsiao-PingTseng and Carl Sechen in their paper “A Gridless Multi-Layer Router forStandard Cell Circuits using CTM Cells” (Proceedings of the 1997European Design and Test Conference, page 319) can be extended to handlediagonal interconnect lines in order to create a gridless non Manhattanrouting tool.

Gridless Non Manhattan Wiring by Compaction

Another method of creating a gridless non Manhattan layout is to compacta gridded non Manhattan wiring layout. The initial gridded non Manhattanlayout may use the gridded non Manhattan wiring with exact intersectionvias or the gridded non Manhattan wiring with inexact intersection viasas described in the earlier sections of this document. The gridded nonManhattan routing is then compacted in both vertical and horizontaldirections to produce a gridless non Manhattan layout that increases theinterconnect line density.

In the resulting gridless non Manhattan interconnect system, anyinterconnect line on any layer may be placed at any location as long asthat signal line does not interfere with other nearby interconnectlines. Similarly, vias used to connect interconnect lines on differentlayers may be placed anywhere that does not cause interference since theinterconnect lines on the different levels may be placed at anyposition. By allowing the positioning of signal lines and vias anywhere,the compacted gridless system of the present invention renders therouting system much more complex.

Gridless Non Manhattan by Compaction Wiring Example

To best illustrate a compacted gridless non Manhattan wiring system, afull example is presented with reference to FIGS. 12, 13 a to 13 l, 14,and 15. FIG. 13 a illustrates a layout section of non Manhattaninterconnect wiring that has not been compacted yet. In the nonManhattan interconnect wiring layout of FIG. 13 a there are tenindividual interconnect lines labeled A through J. The wiring layout ofFIG. 13 a is comprised of three wiring layers with three differentpreferred wiring directions: A horizontal wiring layer with interconnectlines A, B, D and F; a vertical wiring layer with interconnect lines H,I, and J; and a 45° diagonal wiring layer with interconnect lines D, E,and G. Since the different angled wires are on different layers, thewires that appear to cross each other are not electrically connected.The various interconnect lines that connect to form comers are connectedwith vias (not shown). The non Manhattan wiring of FIG. 13 a will becompacted according to the method set forth in the flow diagram of FIG.12.

Referring to FIG. 12, the first step is to create a sorted relativeposition graph of all the horizontal and diagonal interconnect lines asset forth in step 1210. Referring back to FIG. 13 a, this would includeinterconnect lines A, B, C, D, E, F, and G. The sorted relative positiongraph creates a graph of interconnect lines from top to bottom in theirrelative positions. Diagonal lines are considered independent fromhorizontal lines since they reside on a different metal layer. FIG. 14illustrates a sorted vertical relative position graph of all thehorizontal interconnect lines and the diagonal interconnect lines fromFIG. 13 a. Note that the horizontal and diagonal lines are placed intoindependent graphs. Furthermore, the graph of FIG. 14 includes dashedconnectors that indicated that the two interconnect lines are connectedwith a via.

Next, at step 1220, the system selects an independent group ofinterconnect lines from the sorted graph. In this example, theindependent group of horizontal lines A, B, D, and F from the graph ofFIG. 14 is selected. The system then proceeds to step 1230 where itsuccessively compacts each line from the independent group of sortedinterconnect lines. To compact downward, the system first starts withthe bottommost interconnect line F and attempts to move it downward.Since it is already at the bottom, it is not moved. Next, the systemproceeds to the next lowest interconnect line D and compacts it downwardas close to interconnect line F as possible without causinginterference. The result is illustrated in FIG. 13 b.

Next, the system moves the next lowest interconnect line B. However,note that interconnect line B is connected to diagonal interconnect lineC such that interconnect line C must also be moved downward. The resultafter moving both horizontal interconnect line B and diagonalinterconnect line C is illustrated in FIG. 13 c. Finally, the lasthorizontal interconnect line A is compacted downward as close aspossible to interconnect line B. The result after moving both horizontalinterconnect line A downward is illustrated in FIG. 13 d.

Referring back to FIG. 12, after the last horizontal line was compactedthe system proceeds to step 1240 where it determines whether there areany more sorted vertical groups that have not yet been compacted.Referring again to the sorted vertical relative position graph of FIG.14, it can be seen that there is the set of diagonal interconnect linesthat need to be compacted. Thus, the system returns back to step 1220 toselect the diagonal interconnect lines and then to step 1230 tovertically compact the diagonal lines.

The bottommost diagonal interconnect line G is compacted downward first.The result after compacting down diagonal interconnect line G isillustrated in FIG. 13 e. Next, the system compacts down diagonalinterconnect line E. As set forth in FIG. 14, diagonal interconnect lineE is coupled to horizontal interconnect line F such that horizontalinterconnect line F also needs to be adjusted. FIG. 13 f illustrates theresultant routing after diagonal interconnect line E has been compacteddownward. Finally, diagonal interconnect line C needs to be moveddownward. However, diagonal interconnect line E is coupled to horizontalinterconnect line B that has already been compacted down as far as itwill go. Thus, diagonal interconnect line C is not moved and thevertical compaction of diagonal lines at step 1230 is done.

Referring back to FIG. 12, the system then proceeds again to step 1240,at this point all the vertical compaction has complete such that thesystem proceeds to step 1250. At step 1250 the system creates a sortedrelative horizontal position graph of all the vertical interconnectlines and diagonal interconnect lines. FIG. 15 illustrates the outputsorted relative horizontal position graph of all the verticalinterconnect lines and the diagonal interconnect lines. As illustratedin FIG. 15, there are three independent groups interconnect lines. Notethat vertical line J is independent from vertical lines H and I since itdoes not over lap those two vertical interconnection lines in thevertical dimension.

Referring back to FIG. 12, the system selects an independent group ofinterconnect lines from the set of interconnect lines sorted by relativehorizontal positions. In this example, the first group will be verticalinterconnect lines H and I. Thus, at step 1270 vertical interconnectlines H and I are compacted horizontally. In this example, thecompaction is to the right such that interconnect line I is compacted tothe right first as illustrated in FIG. 13 g. Next, the system compactsinterconnect line H to the right as illustrated in FIG. 13 h, thuscompleting the compaction of that group of lines.

The system then moves to step 1280 to determine if additional lines needto be compacted horizontally. Since the answer is “yes”, the systemproceeds to step 1260 where the diagonal lines are selected next and tostep 1270 to compact the diagonal lines. Right most diagonalinterconnect line G is the first to be compacted. The result aftercompacting diagonal interconnect line G to the right is illustrated inFIG. 13 i. Next, diagonal interconnect line E is compacted to the rightis illustrated in FIG. 13 j. Finally, diagonal interconnect line C iscompacted to the right to complete the diagonal line group with the endresult illustrated in FIG. 13 k. Note that only a very small segment ofhorizontal interconnect line B remains. In one embodiment, interconnectline B is completely removed and interconnect line C is then coupleddirectly to interconnect line I.

Referring again to FIG. 12, the system again moves to step 1280 todetermine if additional lines need to be compacted horizontally. Theanswer is again “yes” since vertical interconnect line J still needs tobe compacted. The system thus proceeds to step 1260 where verticalinterconnect line J is selected next and to step 1270 to compactvertical interconnect line J. However, vertical interconnect line Jcannot be compacted anymore. Thus, the system again moves to step 1280to determine if additional lines need to be compacted horizontally. Atthis point there are no more groups to compact such that the compactionis complete. FIG. 13 l illustrates a final view of the compactedrouting.

Compaction Around Obstacles Example

Obstacles in the layout area may limit the space that may be used forcompaction. For example, a licensed circuit module may take a predefinedamount of space. In order to handle such area limitations, thecompaction system must be able to adapt to the available area.

FIGS. 16 a to 16 f illustrate the vertical compaction of interconnectlines around an obstacle 1690. As the horizontal lines are compacteddown, the horizontal interconnect lines may be broken down intosubsections. For example, horizontal line F in FIG. 16 a is broken intotwo different sections 1611 and 1613 as illustrated in FIG. 16 b. Thenew horizontal subsections 1611 and 1613 are then coupled by newlycreated vertical interconnect line section 1612. Newly createdinterconnect lines, such as newly created vertical interconnect linesection 1612, are added into the sorted relative horizontal positiongraph of all the vertical interconnect lines and the diagonalinterconnect lines.

Diagonal interconnect lines may be flattened out during the compactionprocess. Referring again to FIGS. 16 a and 16 b, diagonal interconnectline E is flattened into horizontal subsection 1613. In addition, asecond newly created vertical interconnect line section 1614 is createdto link horizontal subsection 1613 to diagonal subsection 1615.

Euclidean Wiring

Although this document refers to non Manhattan layers that may be of anyangle, many manufacturers would be more comfortable with onlymanufacturing Manhattan wiring or Manhattan and +/−45° angle diagonalwiring. Thus, the present invention introduces the concept of usinggridless Manhattan wiring or gridless Manhattan and +/−45° anglediagonal wiring system to closely approximate a Euclidean wiring systemwherein interconnect lines may be of almost any angle. In contrast, thenumber of angles that may be simulated in a gridded system routingsystem is sharply limited.

Simulated Euclidean with Gridless Manhattan Routing

FIG. 17 a illustrates a small gridded Manhattan interconnect line madeup of horizontal and vertical segments. Specifically, the interconnectline of FIG. 17 a consists of two separate vertical segments and twohorizontal segments that must be on the illustrated detailed routinggrid. The four interconnect line segments of FIG. 17 a simulate a directsignal line with angle A in a gridded Manhattan system. With such agridded Manhattan system, the number of angles that may be representedis sharply limited by the detailed routing grid. For example, the nextsmallest angle that may be represented with vertical change of no morethan two detailed routing grid units is shown in FIG. 17 b, where thehorizontal segment was extended to the next detailed routing gridintersection.

In a gridless Manhattan routing system, almost any angle may berepresented since the signal lines are not restricted to being onspecific detailed routing grid positions. (Note that there still may bea manufacturing grid resolution but that manufacturing grid resolutionis finer than the thickness of an interconnect line.) FIGS. 17 c through17 f illustrate a gridless Manhattan system used to simulate Euclideanwiring. The gridless Manhattan system can represent the same angles asthe gridded system. Specifically, the gridless interconnect lines ofFIGS. 17 c and 17 f illustrate the same angles as in the griddedinterconnect lines of FIGS. 17 a and 17 b. However, the gridlessManhattan system can also be used to simulate almost every angle inbetween. FIGS. 17 d and 17 e illustrate only two of the nearly infinitenumber of possible interconnect line angles between FIGS. 17 c and 17 f.Thus, with the gridless Manhattan routing system, Euclidean wiring maybe accurately simulated. To simplify the manufacturing task, the systemmay limit how short an interconnect line segment may be such that thesimulated Euclidean interconnect lines do not always use themanufacturing grid resolution.

To construct the simulated Euclidean interconnect lines, a slightlymodified version of the well-known Bresenham line drawing algorithm. Therequired modification is to also plot a point at Y+1, X when plotting apoint at X+1, Y+1 such that there is always horizontal or verticalcontinuity along line segments.

Simulated Euclidean with Gridless Non Manhattan Routine

To provide an even better simulation of Euclidean wiring, it would bedesirable to use 45° angle line segments. Manufacturing 45° anglesegments are not a severe stretch from existing manufacturing techniquessince 45° angle segments can be created by moving a single unit in boththe horizontal and vertical directions.

FIG. 18 a illustrates a small gridded non Manhattan interconnect linethat uses 45° angle segments. The interconnect line of FIG. 18 aconsists of two separate 45° angle segments joined by one horizontalsegment. The three interconnect line segments of FIG. 18 a simulate adirect interconnect line with angle A. With a gridded system, the numberof angles that may be represented is limited by the detailed routinggrid. For example, FIG. 18 b illustrates the next smallest angle thatmay be created for an interconnect line that is no more than twodetailed routing grid units high. As illustrated in FIG. 18 b, thehorizontal segment was extended to the next detailed routing gridintersection.

In a gridless non Manhattan routing system, almost any angle may berepresented since the signal lines are not restricted to being onspecific detailed routing grid positions. FIGS. 18 c through 18 fillustrate a gridless non Manhattan system that uses 45° angle segmentsto simulate Euclidean wiring. The gridless non Manhattan system canrepresent the same angles as the gridded non Manhattan system of FIGS.18 a and 18 b. Specifically, FIGS. 18 c and 18 f illustrate a gridlessnon Manhattan implementation of the same wiring illustrated in griddedwiring of FIGS. 18 a and 18 b, respectively. By comparing the gridlessimplementations to the dashed ideal Euclidean line, it can easily beseen that the gridless implementation is much closer to the idealEuclidean line. Note that the interconnect line positions are limited bya “manufacturing grid” imposed by the manufacturing process but thatgrid is very fine (an order of magnitude smaller than the thickness ofthe interconnect wires).

The gridless non Manhattan system can also be used to simulate nearlyevery angle in between the two angles of FIGS. 18 c and 18 f. FIGS. 18 dand 18 e illustrate only two of the infinite possible signal line anglesbetween FIGS. 18 c and 18 f. Thus, with the gridless non Manhattanrouting system, Euclidean wiring may be accurately simulated.

Simulated Euclidean with Non Manhattan Layers

To simulate any angle wiring with non Manhattan layers, oneimplementation of the present invention uses a mix of Manhattan and 45°angle diagonal interconnect lines as shown in FIGS. 18 c through 18 f.For example, to create interconnect lines with an angle between zero andforty-five degrees, the system uses a mix of horizontal and 45° anglediagonal interconnect lines. FIG. 19 a illustrates how an interconnectline of angle A (an angle between zero and forty-five degrees) may besimulated.

FIG. 19 a illustrates a first method of calculating the lengths of thetwo sections. Referring to FIG. 19 a, an interconnect line with angle A(an angle between zero and forty-five degrees) is constructed with ahorizontal interconnect line 1910 segment and a 45° angle diagonalinterconnect line 1920 segment. The interconnect line with angle A has aslope of n/m where y=x*tan(A). To provide a vertical rise of y, a 45°angle diagonal interconnect line 1920 of length √{square root over (2)}yis used. This 45° angle diagonal interconnect line 1920 also provideshorizontal change of y. To provide the remainder of the horizontalchange, a horizontal interconnect line 1910 of length x-y is used (wherex equals the entire horizontal distance change for vertical distancechange of y). Expressed only in terms of angle A and vertical distancey, the horizontal interconnect line 1910 is created with a length ofy*cotan(A)−y=y(cotan(A)−1).

FIG. 19 b illustrates another way of calculating the lengths of the twosections. Referring to FIG. 19 b, an interconnect line with angle A (anangle between zero and forty-five degrees) is constructed withhorizontal interconnect line 1950 segments and 45° angle diagonalinterconnect line 1960 segments. The interconnect line with angle A hasa slope of n/m where n=sin(A)*m. To provide a vertical rise of n, a 45°angle diagonal interconnect line 1960 of length √{square root over (2)}nis used. This 45° angle diagonal interconnect line 1960 also provideshorizontal change of n. To provide the remainder of the horizontalchange, a horizontal interconnect line 1950 of length m-n is used (wherem equals the entire horizontal distance change for vertical distancechange of n). Expressed only in terms of angle A and n, the horizontalinterconnect line 1950 is created with a length of n/sin(A)−n.

The vertical distance change value of n is selected in a manner thatbest allows the manufacturer to manufacture a desired integrated circuitdesign. Specifically, a very small value of n approximates the A degreeinterconnect line very closely but can be difficult to manufacture. Alarge value of n will not closely approximate the desired line with anangle of A.

To closely track the desired interconnect line with an angle of A, thesimulated angle A interconnect line will cross back and forth across theideal Euclidean interconnect line with an angle of A. Specifically, FIG.20 illustrates how alternating pairs of horizontal interconnect lines2010 and diagonal interconnect lines 2020 are used to create a closeapproximation to the desired interconnect line 2080 with angle A.

Simulated Euclidean Layers

With the ability to simulate any arbitrary angle with a combination ofManhattan and 45° angle diagonal interconnect lines, the teachings ofthe present invention can be used to created entire metal layers at anyarbitrary angle. Specifically, a selected metal layer may be designatedto have a preferred direction of any angle. The preferred directioninterconnect lines on that layer are then created by depositing both theManhattan (horizontal or vertical) and 45° angle diagonal interconnectlines on that layer in the proper proportions. For example, FIG. 21illustrates an example metal layer that contains an arbitrary preferredangle layer that is approximated with a collection of Manhattan(horizontal or vertical) and 45° angle diagonal interconnect linesegments on the same layer. Arbitrary angle interconnect line 2120couples circuit 2121 and circuit 2125. Arbitrary angle interconnect line2110 couples circuit 2111 and circuit 2115 with the aid of a verticalinterconnect line segment 2117 on another layer.

With the availability of arbitrary wiring direction layers, theselection of a wiring layer direction becomes a parameter that may beautomatically selected by layout software or hand selected by a layoutengineer. For example, a particular layout may be best wired using awiring layer with a 38.5 degree preferred direction according to alayout program. Thus, such a 38.5 degree preferred direction layer maybe created using the simulated Euclidean wiring technique.

FIG. 22 illustrates three different useful sets of useful wiringdirection layers: (1) HVD₁D₂ comprising Horizontal, Vertical, +45°diagonal, and −45° diagonal, layers; (2) HVD₂D₁ comprising Horizontal,Vertical, Horizontal, −45° diagonal, and +45° diagonal layers; and (3)HVA₁A₂ comprising Horizontal, Vertical, and two arbitrary angle layersthat are selected based up on the particular layout requirements. Thearbitrary angle layers may be implemented with the simulated Euclideanwiring layers disclosed in the previous section. Additional layers canbe added on the four layer systems illustrated in FIG. 22.

FIG. 23 illustrates three additional different useful sets of usefulwiring direction layers: (1) HVHD₁D₂A comprising Horizontal, Vertical,Horizontal, +45° diagonal, −45° diagonal, and one arbitrary selectedlayer; (2) HVHD₂D₁A comprising Horizontal, Vertical, Horizontal, −45°diagonal, +45° diagonal, and one arbitrary selected layer; and (3)HVHA₁A₂A₃ comprising Horizontal, Vertical, Horizontal, and threearbitrary angle layers that are selected based up on the particularlayout requirements. The arbitrary angle layers may be implemented withthe simulated Euclidean wiring layers disclosed in the previous section.

One additional non Manhattan routing system technique to note is asystem that uses diagonal wires in the core lowest layers of the design.Specifically, the lowest layers may be created diagonal relative to theintegrated circuit edge. In has been found that such designs can improvethe density of the overall layout of the design. FIG. 24 illustrates asimplified example of such a design. As illustrated in FIG. 24, circuitmodule 2410 and circuit 2420 diagonal relative to the edges ofintegrated circuit 2400. Similarly, the interconnect line routing wiresare diagonal relative to the edges of integrated circuit 2400.

The foregoing has described methods and apparatus for routinginterconnect lines for an integrated circuit (“IC”) in a gridless nonManhattan manner. It is contemplated that changes and modifications maybe made by one of ordinary skill in the art, to the materials andarrangements of elements of the present invention without departing fromthe scope of the invention.

1. An integrated circuit layout, said integrated circuit layoutcomprising: a plurality of circuit module designs; a first interconnectline layer, said first interconnect line layer having a preferredhorizontal direction of interconnect lines; a second interconnect linelayer, said second interconnect line layer having a preferred verticaldirection of interconnect lines; and a third interconnect line layer,said third interconnect line layer having a first diagonal preferreddirection of interconnect lines; wherein a plurality of interconnectlines on said first second, and third interconnect line layers couplesaid plurality of circuit module designs, said plurality of interconnectlines generated by using gridless routing, said gridless routingresulting in at least one pair of parallel interconnect lines on one ofsaid interconnect line layers being closer than a minimum requiredline-to-via spacing.
 2. The integrated circuit layout as claimed inclaim 1, said integrated circuit layout further comprising: a fourthinterconnect line layer, said fourth interconnect line layer having asecond diagonal preferred direction of interconnect lines, said seconddiagonal preferred direction orthogonal to said first diagonal preferreddirection.
 3. The integrated circuit layout as claimed in claim 2,wherein said first diagonal preferred direction is approximatelyforty-five degrees relative to said preferred horizontal direction andsaid second diagonal preferred direction is approximately negativeforty-five degrees relative to said preferred horizontal direction. 4.The integrated circuit layout as claimed in claim 1, said integratedcircuit layout further comprising: a fourth interconnect line layer,said fourth interconnect line layer having a preferred horizontaldirection of interconnect lines.
 5. The integrated circuit layout asclaimed in claim 4, said integrated circuit layout further comprising: afifth interconnect line layer, said fifth interconnect line layer havinga second diagonal preferred direction of interconnect lines, said seconddiagonal preferred direction orthogonal to said first diagonal preferreddirection.
 6. The integrated circuit layout as claimed in claim 1, saidintegrated circuit layout further comprising: a fourth interconnect linelayer, said fourth interconnect line layer having a second diagonalpreferred direction of interconnect lines; wherein said first diagonalpreferred direction is approximately sixty degrees relative to saidpreferred horizontal direction and said second diagonal preferreddirection is approximately negative sixty degrees relative to saidpreferred horizontal direction.
 7. The integrated circuit layout asclaimed in claim 1, said integrated circuit layout further comprising: afourth interconnect line layer, said fourth interconnect line layerhaving a second diagonal preferred direction of interconnect lines;wherein said first diagonal preferred direction is approximatelynegative sixty degrees relative to said preferred horizontal directionand said second diagonal preferred direction is approximately positivethirty degrees relative to said preferred horizontal direction.
 8. Theintegrated circuit layout as claimed in claim 1, wherein said integratedcircuit layout is formed by compacting a gridded integrated circuitlayout.
 9. The integrated circuit layout as claimed in claim 1, whereinsaid pair of parallel interconnect lines may be placed as close togetheras can be manufactured reliably.
 10. The integrated circuit layout asclaimed in claim 1, wherein vias couple interconnect lines on differentinterconnect line layers.
 11. A method of laying out an integratedcircuit, said method comprising: placing a plurality of circuit moduledesigns; routing a first interconnect line layer, said firstinterconnect line layer having a preferred horizontal direction ofinterconnect lines; routing a second interconnect line layer, saidsecond interconnect line layer having a preferred vertical direction ofinterconnect lines; and routing a third interconnect line layer, saidthird interconnect line layer having a first diagonal preferreddirection of interconnect lines; wherein a plurality of interconnectlines on said first, second, and third interconnect line layers couplesaid plurality of circuit module designs, said plurality of interconnectlines generated by using gridless routing, said gridless routingresulting in at least one pair of parallel interconnect lines on one ofsaid interconnect line layers being closer than a minimum requiredline-to-via spacing.
 12. The method of laying out said integratedcircuit layout as claimed in claim 11, said method further comprising;routing a fourth interconnect line layer, said fourth interconnect linelayer having a second diagonal preferred direction of interconnectlines, said second diagonal preferred direction orthogonal to said firstdiagonal preferred direction.
 13. The method of laying out saidintegrated circuit layout as claimed in claim 11, wherein said firstdiagonal preferred direction is approximately forty-five degreesrelative to said preferred horizontal direction and said second diagonalpreferred direction is approximately negative forty-five degreesrelative to said preferred horizontal direction.
 14. The method oflaying out said integrated circuit layout as claimed in claim 11, saidmethod further comprising: routing a fourth interconnect line layer,said fourth interconnect line layer having a preferred horizontaldirection of interconnect lines.
 15. The method of laying out saidintegrated circuit layout as claimed in claim 14, said method furthercomprising: routing a fifth interconnect line layer, said fifthinterconnect line layer having a second diagonal preferred direction ofinterconnect lines, said second diagonal preferred direction orthogonalto said first diagonal preferred direction.
 16. The method of laying outsaid integrated circuit layout as claimed in claim 11, said methodfurther comprising: routing a fourth interconnect line layer, saidfourth interconnect line layer having a second diagonal preferreddirection of interconnect lines; wherein said first diagonal preferreddirection is approximately sixty degrees relative to said preferredhorizontal direction and said second diagonal preferred direction isapproximately negative sixty degrees relative to said preferredhorizontal direction.
 17. The method of laying out said integratedcircuit layout as claimed in claim 11, said method further comprising:routing a fourth interconnect line layer, said fourth interconnect linelayer having a second diagonal preferred direction of interconnectlines; wherein said first diagonal preferred direction is approximatelynegative sixty degrees relative to said preferred horizontal directionand said second diagonal preferred direction is approximately positivethirty degrees relative to said preferred horizontal direction.
 18. Themethod of laying out said integrated circuit layout as claimed in claim11, wherein said integrated circuit layout is formed by compacting agridded integrated circuit layout.
 19. The method of laying out saidintegrated circuit layout as claimed in claim 11, wherein said pair ofparallel interconnect lines may be placed as close together as can bemanufactured reliably.
 20. The method of laying out said integratedcircuit layout as claimed in claim 11, wherein vias couple interconnectlines on different interconnect line layers.
 21. An integrated circuitlayout, said integrated circuit layout comprising: a plurality ofcircuit modules; a first interconnect line layer, said firstinterconnect line layer having a first preferred direction ofinterconnect lines; a second interconnect line layer, said secondinterconnect line layer having a second preferred direction ofinterconnect lines, wherein said first and second preferred directionsof interconnect lines are neither orthogonal nor parallel; and aplurality of interconnect lines on said first and second interconnectline layers; wherein said plurality of interconnect lines couple saidcircuit modules; wherein said plurality of interconnect lines are notaligned with any grid other than a manufacturing grid.
 22. Theintegrated circuit layout of claim 21, wherein said plurality ofinterconnect lines coupling said circuit modules comprise a route. 23.The integrated circuit layout of claim 21, wherein the angle betweensaid first and second preferred directions is less than ninety degrees.24. The integrated circuit layout of claim 21, wherein the angle betweensaid first and second preferred directions is forty-five degrees. 25.The integrated circuit layout of claim 21, wherein the angle betweensaid first and second preferred directions is one hundred thirty-fivedegrees.